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The Tahoe Unit encompasses the blocks 783 and 827, in the Viosca Knoll area. These blocks are located in the Gulf of Mexico approximately 140 miles ESE of New Orleans and 105 miles south of Mobile, Alabama, in water 1,500ft deep.
The leases were acquired in April 1984 and May 1985 respectively.
The discovery well was drilled in 1984 on Viosca Knoll block 783. Four wells and three sidetracks were drilled to evaluate the discovery.
Development phase I
Tahoe was initially developed using one subsea well, tied back to Shell’s Bud platform, located 12 miles away at Main Pass 252. The subsea tree was originally used on Placid’s Green Canyon 29 project and was refurbished for use at Tahoe.
Oceaneering Production Systems provided engineering, procurement and installation services for the subsea system.
Phase I development cost about $27 million and was designed to produce about 30 million cubic feet of natural gas and 1,000bbl of condensate per day. Phase I production began in January 1994.
Development phase II
A decision to proceed with Phase II development was made in June 1995. The Phase II development consisted of three gas wells and one oil well. The total cost is about $160 million for the wells, facilities and the platform.
One of the gas wells, Viosca Knoll 783 no 5, is a single satellite well, with its own umbilical and two 6in flowlines. The other two gas wells and the oil well are located in a central cluster and share electrohydraulic and chemical-injection umbilicals, via an umbilical termination structure and a hydraulic distribution manifold. The well was completed in June 1996.
Phase Two wells are tied back to new facilities (Bud Lite), located at Main Pass 252. The Bud Lite facilities are located on a new jacket bridge connected to the existing Bud platform.
Bud Lite is a hybrid of a new jacket and older deck and facilities taken from Shell’s Picaroon Field, located at Brazos block Al9, C platform.
McDermott was the contractor for the jacket fabrication, and jacket and deck installation. The platform installation was completed in May 1996.
Production capacity for the Bud Lite facility will be 300 million cubic feet of natural gas per day, 7,000 barrels of condensate and 8,000 barrels of oil per day. Peak production rate for Tahoe II is estimated at around 235 million cubic feet of natural gas per day.
Production from Phase II began in August 1996 from the no 5 well. The three other wells began production in April 1997. Total gross ultimate recovery from Phases I and II is currently estimated at about 120 million barrels of oil equivalent.
First production began in October 1996, with peak production rates of 100 million cubic feet per day. The total cost is about $28 million.
The two central cluster gas wells are daisy-chained, sharing a pair of 6in flowlines. The oil well is served by two 4in / 8in pipe-in-pipe insulated flowlines.
Drilling of the four Phase II wells began in September 1995, using Arethusa’s semisubmersible Concord. All of the wells are horizontal producers.
The wellheads and christmas trees were manufactured by FMC of Houston. The subsea control system was supplied by Kvaerner FSSL of Sugar Land. Both FMC and FSSL are part of an alliance formed by Shell, for the development of deepwater subsea projects. Flowline installation was awarded to Global Plus. Umbilical fabrication and installation was awarded to Coflexip/Stena/Duco.
A new Gulf of Mexico gas-production record was achieved by the South-East Tahoe well when, in November 2008, it produced at a rate of 119 MMCF/day.
South-East Tahoe is a 100% Shell-owned field, discovered in March 1996 and located in Block Viosca Knoll 784.
South-East Tahoe is a single satellite well, tied back to the Bud Lite facility located 13 miles away.
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